Hi ,
Is this account disabled or deleted?
Open Computer Management, locate to Local User and Groups>Users as shown blew, check if your Administrator account has been disable. If so, try enable it again. If it is not listed in Users, it could be deleted, try create a new administrator account.

Best regards
Please remember to mark the replies as answers if they help.
If you have feedback for TechNet Subscriber Support, contact
tnmff@microsoft.com.